Inspection methods for rotor blades of a gas turbine are in particular used for quality assurance during manufacture, but also during maintenance and servicing. Particularly in the case of aircraft gas turbines, so-called “pretwist measurements” are performed on the rotor blade units. To be able to perform such measurements and inspections, the rotor blade unit must be provided with contact surfaces to allow for referenced positioning of the rotor blade unit in a suitable measuring device. Until now, such contact surfaces have been formed on the outer shroud at an axially aft side very close to the axial trailing edge of the rotor blade. This approach of providing a contact surface has involved the problem of the trailing edge being affected, in particular damaged, during the formation of the contact surface. Damage to the leading edge or trailing edge of the rotor blade is, on the one hand, difficult and costly to repair and, on the other hand, if the damage should not be noticed, a damaged leading or trailing edge has a negative effect on the efficiency of the gas turbine.